She was a very skillful witch who earned the wrath of Hecate, the Greek goddess of magic.
According to Aelian's On the Characteristics of Animals, Gale was a talented witch who dealt in herbs and potions.
For this Hecate, the goddess of witchcraft, turned her into a small, "evil" (in the words of Aelian) mustelid bearing her name, gale (a land-marten or polecat).
Martens/polecats were thought to have magical potency in ancient Greece, though not necessarily of the beneficial kind.
[2] Gale's name shares an etymology with that of Galanthis, another mortal woman who was turned into a weasel at the hands of an angered goddess, in this case Hera.